1. Field of the Invention
The present invention relates to thermal printers, and a control method and a control program for thermal printers, in which current dot printing data is corrected based on previous dot history.
2. Description of the Related Art
Thermal printers such as line thermal printers have numerous independently drivable heating elements arrayed in a row, and print by selectively driving the heating elements to emit heat and thereby cause the dot on the opposing thermal paper to change color.
The color change produced in the thermal paper depends upon the amount of heat energy applied to the thermal paper or other recording medium by the heating element. In order to print with consistent quality, the heat energy actually applied from the heating element to the recording medium must be stable.
Printing technologies that consider the recent dot history, and printing technologies that change the heat energy applied by the heating elements to thermal paper having different color layers to produce a particular desired color are also known from the literature. See, for example, Japanese Patent 2,836,584.
Printers of this type increase the pulse width of the heating element drive circuit to apply heat energy of a HIGH level to print one color, and shorten the pulse width to apply heat energy of a LOW level in order to print another color.
Printing gray scale content of just one color also requires varying the pulse width according to the density of the color to be printed.
Understanding this background, a thermal printer that can switch between what is known as a hysteresis (or dot history) control mode enabling high quality monochrome printing by referencing the recent dot history, and a print mode for printing multiple colors, is still desirable.
Plural types of logic circuits that can provide the control needed for each print mode must be provided in order to achieve this type of thermal printer, but the logic cannot be changed after manufacturing if the logic circuits for each print mode are hard wired. As a result, if an improved control method is developed after a printer is manufactured, the improved control method cannot be implemented by printers that have already been manufactured. In addition, a separate logic circuit must be provided for each print mode, and this increases the size of the printer.